487 
1908-9.] A Simple Radioscope and a Radiometer. 
that if the forceps were at a distance from the chamber — that is, in the tube — 
they did interfere with the expansion, but that if they were in the expand- 
ing part of the chamber they did not. Again, when testing the radium 
salt on disc, another similar disc was made but kept free from all radio- 
active matter and its action on the expansion tested before the disc with 
the radium was tried. It is possible that some other method of introducing 
the substance to be tested into the expansion chamber might be devised 
which would give less trouble, but as yet none has been tried. 
When the substance to be tested is introduced into the expansion 
chamber it is evident there are risks of the instrument becoming con- 
taminated either by some of the substance tested escaping from the forceps 
with the rush of air during expansion, or by the emanations given off by 
the bodies tested. Care has therefore to be taken that the bodies tested are 
firmly secured, and the tests quickly made, so that as short a time as 
possible may be given for the emanations to collect. 
(. Issued separately July 21 , 1909 .) 
